Known vehicle systems (e.g., locomotives, automobiles, mining equipment, etc.) may include traction motors that provide tractive efforts to propel the vehicle systems. In some cases, the traction motors may be powered by more than one power source. For example, existing hybrid vehicles may be powered by diesel-driven generators and also by on-board energy storage systems (e.g., battery systems). In other cases, a hybrid vehicle system may be powered by the energy storage system and an external power source, such as overhead lines or third rail. The external power source, however, may not be accessible for the entire route. For example, the overhead lines or the third rail may extend along only a portion of the route. For a vehicle system to continue moving along the route when the external power source is not available, the vehicle system should be able to obtain power from another source.
A known locomotive includes a pantograph that couples to overhead lines. While connected to the overhead lines, electrical power is delivered through the pantograph and through, among other things, a direct current (DC) bus or link to the fraction motor(s). When the locomotive is no longer operably connected to the overhead lines, the locomotive includes an energy storage system that powers the traction motor. The electrical power may be delivered through the same DC bus. However, a number of intermediate electrical components may be coupled between the energy storage system and the traction motor. For instance, the energy storage system may be coupled to the DC bus using multiple components (e.g., filters, rectifiers, transformers, etc.). These multiple components may be configured to galvanically isolate the battery from the DC bus and to convert the voltage of the battery to a different voltage.
These additional intermediate components, however, can significantly increase the cost, maintenance needs, and weight of the vehicle system. With respect to weight, the addition of certain components (e.g., transformers) to a vehicle system may add hundreds of pounds or kilograms to the weight of the vehicle system. Such an addition of weight may not be possible for some vehicle systems (e.g., automobiles), and may be undesirable for other vehicle systems. With respect to locomotives, adding one or more transformers can significantly increase the weight of the locomotive and thereby require additional tractive effort to propel the locomotive. In addition, transformers can consume additional volume in the limited space of a vehicle system.